Maryam Namazie
Human rights activist
I don't remember exactly when I stopped believing in God. Having been raised in a fairly open-minded family in Iran, I had no encounter with Islam that mattered until the Islamic movement took power on the back of a defeated revolution in Iran. I was 12 at the time.

I suppose people can go through an entire lifetime without questioning God and a religion that they were born into (out of no choice of their own), especially if it doesn't have much of a say in their lives. If you live in France or Britain, there may never be a need to renounce God actively or come out as an atheist.

But when the state sends a "Hezbollah" (the generic term for Islamist) to your school to ensure that you don't mix with your friends who are boys, stops you from swimming, forces you to be veiled, deems males and females separate and unequal, prescribes different books for you and your girlfriends from those read by boys, denies certain fields of study to you because you are female, and starts killing in­discriminately, then you have no choice but to question, discredit and confront it - all of it. And that is what I did.

Philip Pullman
Author
The main reason I don't believe in God is the missing evidence. There could logically be no evidence that he doesn't exist, so I can only go by the fact that, so far, I've discovered no evidence that he does: I have had no personal experience of being spoken to by God and I see nothing in the world around me, wherever I look in history or science or art or anywhere else, to persuade me that it was the work of God rather than
of nature.

To that extent, I'm an atheist. I would have to agree, though, that God might exist but be in hiding (and I can understand why - with his record, so would I be). If I knew more, I'd be able to make an informed guess about that. But the amount of things I do know is the merest tiny flicker of a solitary spark in the vast encircling darkness that represents all the things I don't know, so he might well be out there in the dark. As I can't say for certain that he isn't, I'd have to say I am an agnostic.

Kenan Malik
Neurobiologist, writer and broadcaster
I am an atheist because I see no need for God. Without God, it is said, we cannot explain the creation of the cosmos, anchor our moral values or infuse our lives with meaning and purpose. I disagree.

Invoking God at best highlights what we cannot yet explain about the physical universe, and at worst exploits that ignorance to mystify. Moral values do not come prepackaged from God, but have to be worked out by human beings through a combination of empathy, reasoning and dialogue.
This is true of believers, too: they, after all, have to decide for themselves which values in their holy books they accept and which ones they reject.
And it is not God that gives meaning to our lives, but our relationships with fellow human beings and the goals and obligations that derive from them. God is at best redundant, at worst an obstruction. Why do I need him?

Susan Blackmore
Psychologist and author
What reason for belief could I possibly have? To explain suffering? He doesn't. Unless, that is, you buy in to his giving us free will, which conflicts with all we know about human decision-making.

To give me hope of an afterlife? My 30 years of parapsychological research threw that hope out. To explain the mystical, spiritual and out-of-body experiences I have had? No: our rapidly improving knowledge of the brain is providing much better explanations than religious reasoning. To explain the existence and complexity of the wonderful world I see around me? No - and this is really the main one.

God is supposed (at least in some versions of the story) to have created us all. Yet the Creator (any creator) is simply redundant. Every living thing on this planet evolved by processes that require no designer, no plans, no guidance and no foresight. We need no God to do this work. Where would he fit in? What would he do? And why? If he did have any role in our creation, he would have to be immensely devious, finickity, deceitful and mind-bogglingly cruel, which would be a very odd kind of God to believe in. So I don't.

Richard Dawkins
Evolutionary biologist
I don't believe in leprechauns, pixies, werewolves, jujus, Thor, Poseidon, Yahweh, Allah or the Trinity. For the same reason in every case: there is not the tiniest shred of evidence for any of them, and the burden of proof rests with those who wish to believe.

Even given no evidence for specific gods, could we make a case for some unspecified "intelligent designer" or "prime mover" or begetter of "something rather than nothing"? By far the most appealing version of this argument is the biological one - living things do present a powerful illusion of design. But that is the very version that Darwin destroyed. Any theist who appeals to "design" of living creatures simply betrays his ignorance of biology. Go away and read a book. And any theist who appeals to biblical evidence betrays his ignorance of modern scholarship. Go away and read another book.

As for the cosmological argument, whose God goes under names such as Prime Mover or First Cause, the physicists are closing in, with spellbinding results. Even if there remain unanswered questions - where do the fundamental laws and constants of physics come from? - obviously it cannot help to postulate a designer whose existence poses bigger questions than he purports to solve. If science fails, our best hope is to build a better science. The answer will lie neither in theology nor - its exact equivalent - reading tea leaves.

In any case, it is a fatuously illogical jump from deistic Unmoved Mover to Christian Trinity, with the Son being tortured and murdered because the Father, for all his omniscience and omnipotence, couldn't think of a better way to forgive "sin".

Equally unconvincing are those who believe because it comforts them (why should truth be consoling?) or because it "feels right". Cherie Blair ["I'm a believer", New Statesman, 18 April] may stand for the "feels right" brigade. She bases her belief on "an understanding of something that my head cannot explain but my heart knows to be true". She aspires to be a judge. M'lud, I cannot provide the evidence you require. My head cannot explain why, but my heart knows it to be true.

Why is religion immune from the critical standards that we apply not just in courts of law, but in every other sphere of life?

Paula Kirby
Writer
I stopped being a believer when it became clear to me that the various versions of Christianity were mutually contradictory and that none had empirical evidence to support it. From the recognition that "knowing in my heart" was an unreliable guide to reality, I began to explore other types of explanation for life, the universe and everything, and discovered in science - biology, chemistry, physics, cosmology, geology, psychology - answers that genuinely explain, as opposed to those of religion, whose aim is to shroud their lack of substance in a cloak of mystery and metaphor.

All-importantly, these scientific answers, even when tentative, are supported by evidence. That they are also far more thrilling, far more awe-inspiring, than anything religion can offer, and that I find life fuller, richer and more satisfying when it's looked firmly in the eye and wholeheartedly embraced for the transient and finite wonder that it is, is a happy bonus.

Sam Harris
Neuroscientist
The most common impediment to clear thinking that a non-believer must confront is the idea that the burden of proof can be fairly placed on his shoulders: "How do you know there is no God? Can you prove it? You atheists are just as dogmatic as the fundamentalists you criticise." This is nonsense: even the devout tacitly reject thousands of gods, along with the cherished doctrines of every religion but their own. Every Christian can confidently judge the God of Zoroaster to be a creature of fiction, without first scouring the universe for evidence of his absence. Absence of evidence is all one ever needs to banish false knowledge. And bad evidence, proffered in a swoon of wishful thinking, is just as damning.

But honest reasoning can lead us further into the fields of unbelief, for we can prove that books such as the Bible and the Quran bear no trace of divine authorship. We know far too much about the history of these texts to accept what they say about their own origins. And just imagine how good a book would be if it had been written by an omniscient Being.

The moment one views the contents of scripture in this light, one can reject the doctrines of Judaism, Christianity and Islam definitively. The true authors of God's eternal Word knew nothing about the origins of life, the relationship between mind and brain, the causes of illness, or how best to create a viable, global civilisation in the 21st century. That alone should resolve every conflict between religion and science in the latter's favour, until the end of the world.

In fact, the notion that any ancient book could be an infallible guide to living in the present gets my vote for being the most dangerously stupid idea on earth.

What remains for us to discover, now and always, are those truths about our world that will allow us to survive and fully flourish. For this, we need only well-intentioned and honest inquiry - love and reason. Faith, if it is ever right about anything, is right by accident.

Daniel Dennett
Philosopher
The concept of God has gradually retreated from the concept of an anthropomorphic creator figure, judge and overseer to a mystery-shrouded Wonderful Something-or-Other utterly beyond human ken. It is impossible for me to believe in any of the anthropomorphic gods, because they are simply ridiculous, and so obviously the fantasy-projections of scientifically ignorant minds trying to understand the world. It is impossible for me to believe in the laundered versions, because they are systematically incomprehensible. It would be like trying to believe in the existence of wodgifoop - what's that? Don't ask; it's beyond saying.

But why try anyway? There is no obligation to try to believe in God; that's a particularly pernicious myth left over from the days when organised religions created the belief in belief. One can be good without God, obviously.

Many people feel very strongly that one should try to believe in God, so as not to upset Granny, or so as to encourage others to do likewise, or because it makes you nicer or nobler. So they go through the motions. Usually it doesn't work.

I am in awe of the universe itself, and very grateful to be a part of it. That is enough.

A C Grayling
Philosopher
I do not believe that there are any such things as gods and goddesses, for exactly the same reasons as I do not believe there are fairies, goblins or sprites, and these reasons should be obvious to anyone over the age of ten.

Steven Weinberg
Nobel laureate in physics
I do not believe in God - an intelligent, all-powerful being who cares about human beings - because the idea seems to me to be silly. The positive arguments that have been given for belief in God all appear to me as silly as the proposition they are intended to prove. Fortunately, in some parts of the world, religious belief has weakened enough so that people no longer kill each other over differences in this silliness.

It is past time that the human race should grow up, enjoying what is good in life, including the pleasure of learning how the world works, and freeing ourselves altogether from supernatural silliness in facing the real problems and tragedies of our lives.

Peter Atkins
Chemist
In part because there is no evidence for a God (sentimental longing, desperation, ignorance and angst are not evidence) and in part because science is showing that it is capable of answering all the questions that the religious have argued, without any evidence, require the activities of a God, I dismiss holy scripture as evidence. I also discount the argument that a majority of people in the world claim to be believers, because truth is not decided by majority vote.

I acknowledge the power of cultural conditioning, especially when it is larded on to the young and impressionable, and can even accept that there might be an evolutionary advantage in believing; but neither is an argument for the truth of the existence of a God. Moreover, the horrors of the world, both personal and societal, do not convince me that the creation is an act of infinite benevolence.

Jim al-Khalili
Theoretical physicist
It is often said that religious faith is about mankind's search for a deeper meaning to existence. But just because we search for it does not mean it is there. My faith is in humanity itself, without attaching any metaphysical baggage.

Sir Roger Penrose
Physicist
I don't believe in the dogmas of any religion (or any that I have ever heard of), because the associated myths sound far too fanciful and arbitrary for them to have any credibility, in my opinion. If you ask me about a belief in some more abstract notion of "God", I would, of course, have to know what you mean by such a term.

I suppose the closest I could get to anything that bears any relation to the kind of notion that the term "God" might be used for would be something along the lines of Platonist ideals. These could include some sort of objective moral standpoint that is independent of ourselves, and not simply definable in terms of what might be of benefit to human society. This would imply, for instance, that conscious beings such as elephants would have rights, in addition to those of humans.

I am also prepared to accept that there might be objective ("Platonic") elements involved in artistic achievement, and certainly I assign a Platonic objectivity to truth (especially unambiguous mathematical truth). But I am not at all sure that it is helpful to attach the term "God" to any of this. Moreover, thinking of God as a benevolent creator is particularly misleading, as is made clear, in my opinion, by the problem of the existence of evil - or natural, indiscriminate calamity.

If "God" is to be a sentient being of some sort, I also find that incredible. A conscious being would have to be one that I could just about imagine myself being. I certainly cannot imagine myself being "God"!

Ben Goldacre
Science writer
I think probably the main answer to your question is: I just don't have any interest either way, but I wouldn't want to understate how uninterested I am. There still hasn't been a word invented for people like me, whose main ex­perience when presented with this issue is an overwhelming, mind-blowing, intergalactic sense of having more interesting things to think about. I'm not sure that's accurately covered by words such as "atheist", and definitely not by "agnostic". I just don't care.

Polly Toynbee
Journalist and president, British Humanist Association
The only time I am ever tempted, momentarily, to believe in a God is when I shake an angry fist at him for some monstrous suffering inflicted on the world for no reason whatever. The Greeks and Romans and other pagans probably produced the most convincing gods - petulant, childish, selfish - demanding sacrifices to their vanity and inflicting random furies. At least that's a logical explanation. But an all-powerful God of goodness and love is evidently impossible. He would be a monster. Voltaire said so after the Lisbon earthquake.

Victor Stenger
Particle physicist
I not only do not believe in God, I am almost 100 per cent certain the God of Abraham worshipped by Jews, Christians and Muslims does not exist. This God supposedly plays such an important role in the universe that there should be evidence he exists. There is nothing in the realm of human knowledge that requires anything supernatural, anything beyond matter, to describe our observations.
Furthermore, religion is immoral. It is bad for individuals and bad for society.

Jerry Coyne
Biologist
There is simply no good data pointing to a supernatural being who either takes an interest in the world or actively affects it. Isn't it curious that all the big miracles, resurrections and ascensions to heaven occurred in the distant past, documented by single, dubious books? Besides, the "truth claims" of the various faiths about prophets, virgin births, angels, heaven and the like are not only scientifically unbelievable, but conflicting, so that most or all of them must be wrong. To Christians, Jesus is absolutely the scion and substance of God; to Muslims, that's blasphemy, punishable by execution.

The more science learns about the world, the less room there is for God. Natural selection dispelled the last biology-based argument for divinity - the "design" of plants and animals. Now physics is displacing other claims, showing how the universe could have begun from "nothing" without celestial help.

There's not only an absence of evidence for God, but good evidence against him. To the open-minded, religions were clearly invented by human beings to support their fervent wishes for what they wanted to be true.

Our very world testifies constantly against God. Take natural selection, a process that is cruel, painful and wasteful. After Darwin's idea displaced Genesis-based creationism, the theological sausage-grinder - designed to transform scientific necessities into religious virtues - rationalised why it was better for God to have used natural selection to produce human beings. Needless to say, that argument doesn't fit with an all-loving God. Equally feeble are theological explanations for other suffering in the world. If there is a God, the evidence points to one who is apathetic - or even
a bit malicious.

To believers, testing the "God hypothesis" is not an option because they will accept no observations that disprove it. While I can imagine scientific evidence for God, even evidence that would make me a believer (a reappearing Jesus who instantly restores the limbs of amputees would do), there is no evidence - not even the Holocaust - which can dispel their faith in a good and loving God.

Stephen Hawking
Physicist
I am not claiming there is no God. The scientific account is complete, but it does not predict human behaviour, because there are too many equations to solve.One therefore uses a different model, which can include free will and God.

Michael Shermer
Publisher of Skeptic magazine
I do not believe in God for four reasons. First, there is not enough evidence for the existence of an omniscient, omnipotent being who created the universe and ourselves and hands down moral laws and offers us eternal life. Second, any such being that was supernatural would by definition be outside the purview of our knowledge of the natural world and would necessarily have to be part of the natural world if we did discover such an entity. This brings me to the third reason, Shermer's Last Law, which is that any sufficiently advanced extraterrestrial intelligence is indistinguishable from God. (Because of Moore's law [of increasing computer power] and Kurzweil's law of accelerating returns, we ourselves will be able to engineer life, solar systems and even universes, given enough time.) Fourth, there is overwhelming evidence from history, anthropology, sociology and psychology that human beings created God, not vice versa. In the past 10,000 years there have been roughly 10,000 religions and 1,000 different gods. What are the chances that one group of people discovered the One True God while everyone else believed in 9,999 false gods? A likelier explanation is that all gods and religion are socially and psychologically constructed. We created gods.

John Harris
Bioethicist
There is no good reason to believe that anything that could coherently be called God exists. A rational person does not waste time believing or even being agnostic about things that there are no good reasons to accept. Even if there was a more powerful being (or, more likely, society or planet of beings) than ourselves with a technology that could have created even our solar system and everything in it, that would not give us anything but prudential and scientific reasons to take any notice of them whatsoever - certainly no reason to worship them.

Bertrand Russell pointed out long ago that the moral character of the Judaeo-Christian God as revealed in the writings of his sycophants leaves much to be desired. The same seems to go for other gods as well. So God is not only non-existent, but also wicked and useless.

Jennifer Bardi
Editor of the Humanist
The short and easy answer is lack of evidence. I also see no value in believing in God, because if you're thinking clearly and honestly you necessarily must face the issue of suffering, and the ensuing existential crisis wastes precious time and energy. Alleviating suffering is what we should pour our minds and hearts into.

Moreover, I simply don't want to believe, because the notion of an all-knowing, all-seeing God who lets bad stuff happen really gives me the creeps.

Richard Wiseman
Psychologist
I do not believe in God because it seems both illogical and unnecessary. According to the believers, their God is an all-powerful and almighty force. However, despite this, their God allows for huge amounts of suffering and disease. Also, if I were to believe in God, logically speaking I would have to believe in a wide range of other entities for which there is no evidence, including pixies, goblins and gnomes, etc. It's a long list and I don't have room in my head for all of them. So, I am happy to believe that there is no God. We are just insignificant lumps of carbon flying through a tiny section of the universe. Our destiny is totally in our own hands, and it is up to each of us to make the best of our life. Let's stop worrying about mythical entities and start living.

P Z Myers
Biologist
I am accustomed to the idea that truth claims ought to be justified with some reasonable evidence: if one is going to claim, for instance, that a Jewish carpenter was the son of a God, or that there is a place called heaven where some ineffable, magical part of you goes when you die, then there ought to be some credible reason to believe that. And that reason ought to be more substantial than that it says so in a big book.

Religious claims all seem to short-circuit the rational process of evidence-gathering and testing and the sad thing is that many people don't see a problem with that, and even consider it a virtue. It is why I don't just reject religion, but actively oppose it in all its forms - because it is fundamentally a poison for the mind that undermines our critical faculties.

Religious beliefs are lazy jokes with bad punchlines. Why do you have to chop off the skin at the end of your penis? Because God says so. Why should you abstain from pork, or shrimp, or mixing meat and dairy, or your science classes? Because they might taint your relationship with God. Why do you have to revere a bit of dry biscuit? Because it magically turns into a God when a priest mutters over it. Why do I have to be good? Because if you aren't, a God will set you on fire for all eternity.

These are ridiculous propositions. The whole business of religion is clownshoes freakin' moonshine, hallowed by nothing but unthinking tradition, fear and superstitious behaviour, and an establishment of con artists who have dedicated their lives to propping up a sense of self-importance by claiming to talk to an in­visible big kahuna.

It's not just fact-free, it's all nonsense.

Andrew Copson
Chief executive, British Humanist Association
I don't believe in any gods or goddesses, because they are so obviously human inventions. Desert-dwellers have severe, austere and dry gods; suffering and oppressed people have loving and merciful gods; farmers have gods of rain and fruitfulness; and I have never met a liberal who believed in a conservative God or a conservative who believed in a liberal one. Every God I have ever heard of bears the indelible marks of human manufacture, and through history we can explain how and why we invented them.